29.10 : Glomerular Filtration: Net Filtration Pressure

Glomerular filtration depends on three main pressures: glomerular blood hydrostatic pressure or GBHP, capsular hydrostatic pressure or CHP, and blood colloid osmotic pressure or BCOP.

GBHP, typically about 55 mmHg, is the blood pressure inside the glomerular capillaries. It promotes filtration by pushing water and solutes through the filtration membrane.

CHP, averaging around 15 mmHg, is a back pressure exerted against the filtration membrane by fluid already present in the capsular space and renal tubule, which opposes filtration.

Additionally, BCOP in glomerular capillaries also opposes filtration. It averages 30 mmHg.

The net filtration pressure or NFP is the total pressure that promotes filtration.

It's calculated as NFP = GBHP - CHP - BCOP. Normal NFP is usually about ten mmHg.

In certain kidney diseases, glomerular capillaries can be damaged, allowing plasma proteins to enter the filtrate. This increases the NFP, leading to more fluid being filtered.